The Lambda Bestiary

A moonlit field guide to pure functions, folded rooms, and creatures that live inside type signatures.

summon ::

:: -> => <> where

I / thunk nursery

Lazy Nest

Under dotted blankets sleeps the evaluation beast. Its footprints appear before its body; its name is not demanded until the cave asks for it.

footprint :: Need -> Value
footprint = trace "..." sleepingBeast

->

Functor Aviary

The map-bird carries a value through its violet ribs and returns it changed but still nested in the same kind of sky.

fmap :: (a -> b) -> f a -> f b

a

<>

b

map map fmap <$> map map fmap

Monad Marsh

Here the bind-chain ripples from pool to pool. Each step chooses the next creature by the glow left behind by the last.

(>>=) :: m a -> (a -> m b) -> m b

>>=>>=>>=>>=

IV / reliquary

Typeclass Reliquary

Tiny familiars patrol the old theorem shelves. When a monster proves its habit, a badge fastens itself to the hide with a gold click.

class Show a where
  show :: a -> String

data Beast a = Horn a | Wing a | Tail a

final chamber

REPL Bonfire

The monsters gather around a glowing prompt. Syntax sparks rise into the roof of the cave, becoming constellations of operators and small, precise myths.

λ> explore bestiary